Many of today's handheld devices make use of wireless “connections” for telephony, digital data transfer, geographical positioning, and the like. Despite differences in frequency spectra, modulation methods, and spectral power densities, the wireless connectivity standards use synchronized data packets to transmit and receive data.
In general, all of these wireless-connectivity capabilities (e.g. WiFi, WiMAX, Bluetooth, etc.) are defined by industry-approved standards (e.g. IEEE 802.11, IEEE 802.16) and cellular industry consortium-based standards (e.g. 3GPP LTE) which specify the parameters and limits to which devices having those connectivity capabilities must adhere.
At any point along the device-development continuum, it may be necessary to test and verify that a device is operating within its standards' specifications. Most such devices are transceivers, that is, they transmit and receive wireless RF signals. Specialized systems designed for testing such devices typically contain subsystems designed to receive and analyze device- transmitted signals, and to send signals that subscribe to industry-approved standards so as to determine whether a device is receiving and processing the wireless signals in accordance with its standard.
In the development of radio technology, one advancement of several forms of smart antenna technology includes multiple-input and multiple-output, or MIMO. MIMO utilizes multiple antennas at both the transmitter and receiver (either or both) to improve communication performance; i.e., in order to multiply throughput of a radio link, multiple antennas (and multiple RF chains accordingly) are put at both the transmitter and the receiver. A MIMO system with a similar count of antennas at both the transmitter and the receiver in a point-to-point (PTP) link is able to multiply the system throughput linearly with every additional antenna under favorable conditions. For example, a 2x2 MIMO can double the throughput.
MIMO may employ Spatial Multiplexing (SM) to enable signals (coded and modulated data stream) to be transmitted across different independent spatial domains. Meanwhile, Mobile WiMAX supports multiple MIMO modes, that's using either SM or STC (Space Time Coding) or both to maximize spectral efficiency (increase throughput) without shrinking the coverage area. The dynamic switching between these modes based on channel conditions is called Adaptive MIMO Switching (AMS). If combined with an AAS (Adaptive Antenna System), MIMO can further boost WiMAX performance.
With the advent of bandwidth-hungry broadband users, it has become desirable to implement MIMO technology within many wireless technologies (e.g., PAN, LAN, MAN, and WAN) to address an ever-growing need to increase data rates multiple times. MIMO technology has attracted attention in wireless communications, because it offers significant increases in data throughput and link range without additional bandwidth or transmit power. It achieves this by higher spectral efficiency (more bits per second per hertz of bandwidth) and link reliability or diversity (reduced fading). Because of these properties, MIMO is an important part of modern wireless communication standards such as IEEE 802.11n (Wifi), 4G, 3GPP Long Term Evolution (LTE), WiMAX and HSPA+.
At some point, it is necessary to test and verify a device designed for employing a MIMO system. For example, FIG. 1 illustrates a conventional system 100 employing a standard for fully testing a 2x2 MIMO wireless MIMO device using synchronized 103 vector signal generators (VSGs) 102, 104. In the case of a device 106 designed for two RX/two TX MIMO (e.g. 2x2 MIMO), one could fully test its physical-layer (PHY) characteristics using a testing system having two vector signal analyzers (VSAs) for testing concurrently the two MIMO TX signals. In addition, one could also test using two VSGs for simulating two independent TX MIMO signals for testing the device's two receivers.
In this manner, one is able to test the RX1/digital signal processor (DSP) chain and the RX2/DSP chain of a device under test (DUT) 106 to determine if it is working properly. Having verified the correct operation of the 2x2 DUT's two receive chains using two VSGs, the conventional method may also allow both the verification of the RX chains and MIMO channel estimation. However, the cost of a test system is generally dominated by the costs of the implemented equipment, such as the VSAs and VSGs employed in this instance. Hence, as a practical matter, the more testing equipment employed within a wireless-connectivity test system, the more expensive the aforementioned system tends to be. Furthermore, there may also be expenditures associated with each piece of testing equipment for checking reliability and/or maintenance applications. It would, therefore, be desirable to reduce expenditures related to devices utilized in testing systems while still maintaining reliable testing methods of the implemented equipment.
Attempts have been made to address limiting the components of testing equipment, and hence, the associated cost factors. For example, the conventional embodiment of FIG. 2 employs a testing system 200 by simply taking a single VSG 202 and splitting 204 its output into two identical signals. However, this procedure does not adequately test the capabilities of the two DUT receivers 206, 208. Attempting to use a single VSG 202, in this manner, by splitting the output to provide verification of the RX chain and channel estimation fails to verify both RX chains. This is because, inter alia, the employed procedure merely measures the average of the resulting two noise figures rather than each individual noise figure. As a result, the instant method does not verify the channel estimation which is critical to proper processing of spatial multiplexing (SM) in a MIMO system. In short, the method fails to provide a complete accounting of the testing signal by fully testing both RX1/DSP and RX2/DSP chains. Thus, one would only verify a single DSP chain (instead of the two) and also fail to verify MIMO channel estimation.
Accordingly, a need exists for an improved reduced-cost testing system which meets or exceeds the requirements of leading wireless-connectivity capabilities. This need provides an improved functionality to test manufactured 2x2, 3x2 and 4x2 MIMO wireless devices. A further need exists to reduce the reliance on additional testing equipment, thereby reducing operational costs, to perform tests for identifying defects in wireless equipment and determine block error rate information.